The present invention relates generally to a zoom lens and an imaging system using the same, and more particularly to a zoom lens with the optical axis of its optical system bent and an imaging system incorporating the same.
In recent years, digital cameras (electronic cameras) have received attention as the coming generation of cameras, an alternative to silver-halide 35 mm-film (135-format) cameras. Currently available digital cameras are broken down into some. categories in a wide range from the high-end type for commercial use to the portable low-end type.
In view of the category of the portable low-end type in particular, the primary object of the present invention is to provide the technology for implementing easy-to-use, high-zoom-ratio, less costly video or digital cameras whose depth dimension is reduced while high image quality is ensured, and which have zoom ratios high enough to cover a wide focal length range from the wide-angle end to the telephoto end.
The gravest bottleneck in diminishing the depth dimension of cameras is the thickness of an optical system, especially a zoom lens system from the surface located nearest to its object side to an imaging plane. The technology currently in vogue for slimming down camera bodies makes use of a so-called collapsible lens mount that allows the optical system to be taken out of the camera body for shooting and received therein for carrying around.
However, the use of the collapsible lens mount is not preferable in view of ease of operation, because some time is taken for sending the zoom lens received at it ready for use. Making the lens group nearest to the object side movable is again not preferable for prevention of entrance of moisture and dust. More recent years have seen a camera version that takes no waiting time for sending it ready for use (for booting a zoom lens up); it works favorably for prevention of entrance of moisture and dust and is much more slimmed down in its depth direction by use of an optical system with an optical path (optical axis) bent by a reflecting optical member such as a mirror or a prism. In a typical camera of this version, the lens group nearest to the object side of the zoom lens is fixed in terms of position and the reflecting optical member is received in that lens group, so that the subsequent optical path is bent longitudinally or transversely with respect to a camera body, thereby reducing the depth-direction dimension as much as possible.
For the time being, most video or digital cameras under the portable category to which the invention is directed would have a half angle of view of about 30° at the wide-angle end; however, wide-angle cameras having a greater taking range will come out anyway.
For instance, Patent Publication 1 comes up with a typical wide-angle zoom lens relying upon a bent optical system. However, that zoom lens has a half angle of view of as large as about 37°, yet the zoom ratio remains at barely about 2.8. On the other hand, the zoom lens of Patent Publication 2 has a half angle of view of about 37° and a zoom ratio of about 3.7, yet its full length is still long.
Patent Publication 1
JP(A)2004-354871
Patent Publication 2
JP(A)2004-354869